The present invention relates to gearboxes, and, in particular, to a deoiler portion of a gearbox.
A typical gas turbine engine for an aircraft is coupled to a shaft that drives other shafts via a connection to a gearbox. As the air flows through the gearbox housing, a certain amount of oil naturally becomes entrained in the air and it is desirable that this oil be separated from the air before the air is vented from the gearbox. In some cases, bearing compartments in the turbine are vented into the gearbox and increase the amount of oil in the air in the gearbox.
In order to separate the oil from the air, a deoiler is included in the gearbox. In general, the deoiler includes a separator unit that utilizes centrifugal forces to separate the heavier oil from the lighter air. In some cases, the deoiler includes a shaft on which the separator unit is attached and that include an outlet through which air can be exhausted to the environment.
When the engine is in operation driving the deoiler, pressure greater than atmospheric builds up within the gearbox and because of the high speed rotating gears within the gearbox, oil becomes entrained with the air in chamber. As mentioned above, oil can also be introduced from the bearing compartments due to air that leaks into the bearing compartments from the higher pressure sections of the engine (e.g., compressors and turbines). It is often desirable to minimize the pressure in the gearbox and bearing compartments to help balance the pressure forces on the seals to help avoid blowing engine lubricating oil out of the bearing compartments into the lower pressure sections of the compressor, or turbine. For this reason a low pressure drop across the deoiler in general and the separating unit in particular is usually desired as this pressure drop biases the bearing compartment and gearbox pressure upward. That is, if there is a large pressure drop across the separating unit, the pressure in the gearbox must be increased to drive air into it. It is also advantageous to minimize the size (envelope) and weight of the separating unit. However to achieve the desired pressure drop performance, the size is often increased beyond the size needed to obtain the desired air-oil separation.